During a battle in the way of Allah (swt), sayyedina Ali, found himself face to face with a kafir who attacked him violently. They were both brave and powerful men, but the kafir was no match for sayyedina Ali, who soon was sitting astride his chest, ready to finish him off.
"I invite you to bear witness that there is no god except Allah, and Muhammad is the Messenger of Allah," said Ali. "Accept Islam, and your life will be spared."
"Never!" panted the kafir.
Sayyidina Ali lifted his sword and was just about to plunge it into his enemy, when the kafir spat defiantly in his face.
Much to the kafir's surprise, sayyidina Ali immediately jumped away from his enemy and lowered his sword.
"Go away!" said sayyidina Ali, "I cannot kill you now."
"Why did you do that?" asked the kafir. "You could have killed me easily."
"I was fighting you purely in the way of Allah," replied Ali, "but when you spat in my face, your insult made me angry and if I had killed you in anger, it would have taken me to the Hell Fire - so I had no choice but to let you go. To kill someone in anger or out of desire for revenge is not bravery, but the act of a coward."
On hearing this, the kafir was so impressed by sayyidina Ali's sincerity and self-control that he embraced Islam on the spot: "I bear witness that there is no god but Allah," he said, "and I bear witness that Muhammad is the Messenger of Allah"
May Allah give us sincerity and clean our hearts.
Source: From the book "True stories for children" by Matina Wali Muhammad